Methods employed in conventional pixel interpolation circuits to calculate interpolation data for missing pixels include a method in which the mean of the values of the pixels adjacent to a missing pixel is used as the interpolation data, a method in which a regression line is found for the pixels adjacent to a missing pixel by use of the least squares method and the interpolation data are calculated from the regression line, and a method in which a quartic curve is found from the four pixels adjacent to a missing pixel and the interpolation data are calculated from its quartic equation (see, for example, Patent Document 1).
Patent Document 1: Japanese Patent Application Publication No. 2003-101724 (paragraphs 0040 to 0066, FIGS. 3 to 5)